The invention relates to a process for forming a metal or alloy layer on an electrically-conducting work piece by means of a glow discharge, where the work piece is connected as one electrode of an electric field in a low-pressure chamber loaded with carrier gas, whereby the carrier gas and the material to be coated or spender medium are preionized and are transported in ionized state into the electric field of the low-pressure chamber, as well as a device for the execution of same.
The work pieces to which such a layer is to be applied were hitherto subjected for this purpose to a galvanic bath containing acids or caustic solutions for various treatment times.
This galvanizing process presents the disadvantage that it will give rise to an environmental problem of increasingly greater scope due to the acids or caustic solutions required. Very high investment costs are at least necessary to neutralize the resulting waste waters, provided the pertinent authorities do not forbid the construction of such plants in advance.
High waste-water deliveries result because of the elevated salt load of the neutralized waste waters. To be sure, processes have already been disclosed in which formation of a metal layer on an electricity-conducting work piece takes place by means of a glow discharge, whereby the work piece is connected as one electrode of an electric field in a low-pressure chamber loaded with carrier gas, whereas the other electrode consists of the coating metal. These techniques were not found to be very suitable, as they only make the coating of wires or smaller work pieces possible and, because of the low energy of the impact ions, only with extremely thin and not very adherent layers.
For the sake of completeness of presentation, the so-called gas-plating technique is also mentioned, in which the metal used to form the layer is deposited onto the work piece from a gas containing a suitable metal compound or which consists of same, but the work piece must be highly heated for the purpose. Such high temperatures (temperatures of 1,200.degree. C. or more are involved) impair the physical properties of the work pieces, so that application of the gas-plating technique is very limited.
The task arose of developing a process and a device capable of avoiding the above mentioned disadvantages of the known processes of this type, i.e., which is not harmful to the environment and is also suitable for the production of thick layers on larger work pieces, whereby heating of work pieces up to temperatures injurious to them is avoided.